Method of removing fatty acid coating from iron ores



United States Patent 3,430,763 METHOD OF REMOVING FATTY ACID COATING FROM IRON ORES Iwao Iwasaki, Minneapolis, Minn., assignor to The Regents of the University of Minnesota, Minneapolis, Minn., a corporation of Minnesota No Drawing. Filed Jan. 10, 1967, Ser. No. 608,269 US. Cl. 209- 8 Claims Int. Cl. B03b 1/04 ABSTRACT OF THE DISCLOSURE A method of removing fatty acid coatings from iron ore concentrate resulting from flotation processes by the use of activated canbon. The ore is repulped, conditioned with activated carbon and then removal of fatty acid coatings facilitates further concentration in duplex flotation processes and facilitates pelletizing of the concentrate.

This invention relates to the beneficiation of iron ores by flotation and more particularly to a two-stage or duplex flotation process suitable for use on iron ore fines. Sorne ores must be finely ground in order to free the iron minerals from the siliceous gangue. Other fines result as waste products from other iron ore beneficiation processes.

Increasing amounts of lower grade iron ores are of industrial importance because of the constantly decreasing amounts of available high grade ore. Most of these ores are too low in iron and too high in silica bearing gangue to be suitable for use in blast .furnaces. In order for such ores to be useful, it is necessary to raise the iron content to as high a degree as feasible by reducing the impurities, principally silica. Flotation is one of the most useful methods of separating the gangue from the mineral values. Commonly the iron mineral values are floated from the silica by use of an anionic reagent of the higher aliphatic fatty acid type, among which are oleic acid, fish oil fatty acids, cocoanut oil fatty acids, linseed oil fatty acids, cotton seed oil fatty acids, resin acids, naphthenic acids, tall oil and the like.

In a duplex flotation process the fatty acid flotation of iron minerals is followed by an amine flotation of the siliceous gangue from the rougher iron concentrate. In the first stage a major portion of the iron minerals, together with a part of the gangue, is floated away from the remainder of the ore. In the second stage of the process a major portion of the remaining silica is floated away and the tailing from this operation constitutes the finished product or iron concrentrate.

In order to carry out the duplex floatation, it is necessary that the concentrate from the fatty acid flotation be treated with a suitable surface modifying agent adapted to overcome the effect of the anionic reagent without destroying the potential flotability of the silica. A number of treatments have been proposed for removal of fatty acid coatings from iron oxide surfaces. These include combinations of reagents such as lime and quebracho, lime and alkali phosphate and sulfuric acid and oxalic acids. It has now been discovered that activated carbon is particularly effective in removing fatty acid coatings.

It is necessary that finely divided iron concentrates be re-agglomerated before introduction to the blast furnace. Commonly this is done by forming the concentrate into balls and subjecting the balls to heat to cause a partial fusion of abutting particle surfaces to form a hard spherical ball capable of withstanding handling, storage, shipping, etc., before introduction to the blast furnace. The presence of fatty acid coatings on iron flotation concentrates have in most instances proven undesirable for successful pelletizing.

Activated carbon was evaluated for the removal of a fatty acid coating from iron oxide surfaces using both oxidized iron ore and magnetic .aconite concentrate. In the tests with oxidized iron ore a heavy media separator concentrate from hand picked relatively high grade lumps of ore from the Western Mesabi Range of Minnesota were crushed and pulverized through 65-mesh. The ore thus prepared analyzed 51.4 percent iron. The magnetic taconite concentrate used had a size consisting of 90 percent passing 325-mesh and analyzed 64.5 percent iron. In each test the ore was pulped in water to about 25 to 50 percent solids. Several of the common parameters, such as the amount of fatty acid used in the rougher flotation step, the amount of activated carbon, the conditioning time, the temperature, and the pH were investigated. In this investigation Darco Grade HDB activated carbon supplied by Atlas Chemical Industries, Inc., Wilmington, Del., was used.

Tests with oxidized iron ore FOR DEPRESSING OF A FATTY ACID FLOATED OXI- DIZED IRON ORE USING ACTIVATED CARBON Factors.-X2=act1vated carbon, lb. per ton; Xz=c0nditioning time,

minutes Resp0nse.Y1= percent weight recovery in cell product; Yz=percent iron recovery in cell product AND PRODUCT DATA Design levels Factor levels Response X1 X2 X1 X2 Y1 Y2 To investigate the effects of the levels of activated charcoal addition and conditioning time on the depression of the froth product, a hexagonal experiment was designed as shown in Table 1. After a few preliminary tests the activated carbon was limited to a range of three to eleven pounds per ton and the conditioning time to a range of 3.5 to 10.5 minutes. The flotation results were fitted with a second order regression equation by the method of least squares. An F-test was used to compare the lack of fit variance with the experimental error variance. Although the experimental error was considerably smaller than the lack of fit variance, the multiple correlation coeflicient, based on four degrees of freedom, was 0.9-7. Therefore, the equation was considered to represent the experimental results satisfactorily.

Response contours plotted from the experimental data show that the iron recovered in the cell product, which is a reflection of the removal of the fatty acid coating, is strongly dependent on the amount of activated carbon. The effect of the conditioning time is not pronounced but a long conditioning somewhat helps to depress the iron mineral. In another series of tests (see Table 2, test #3) a thirty minute conditioning with seven pounds of activated carbon per ton results in a noticable increase in the weight of the iron recovered in the cell product.

The results listed in Table 2 also show the effects of the pulp temperature and the pH used in the rougher flotation. Both parameters exert a significant effect on the flotatability after the activated carbon treatment. A higher temperature during the conditioning step facilities the removal of the fatty acid coating. The flotatability of the iron minerals decreases appreciably when the pulp is cooled to room temperature for flotation. When the pulp temperature is held at the same temperature of 60 C. for both conditioning and flotation steps, however, much of the iron minerals reports in the froth product. The pH of the pulp in the flotation step appears to be quite critical. 10 the cell products.

TABLE 2.-EFFECTS OF ACTIVATED CARBON PULP TEMPERATURE, pH AND THE AMOUNT OF FATTY ACID COATING ON AN OXIDIZED IRON ORE Recovery in Fatty Activated Conditioning Flotation 0011 product Test No acid carbon (UL/ton) (lb./ton) Temp., C. Time, min. Temp., C. pH Percent wt. Percent Fe 1 2. O 7 60 7 60 8 33. 87 31. 23 2. 7 00 7 28 8 94. 17 94. 42 2. 0 7 RT 30 RT 8 92. 47 93. 20 2. 0 7 RT 7 RT 22. 02 21. 84 0. 5 3 RT 7 RT 8 90. 28 90. 50 0. 5 l. 5 RT 7 RT 8 26. 39 22. 71

When the pH is adjusted to 10, nearly 77 percent by weight of the iron oxides floats, whereas only percent floats if the pH is kept at the natural pH of the conditioned pulp of 8.0 to 8.1. Evidently the activated carbon releases some alkaline material which raises the pH of the pulp to near 8.

Table 2 also indicates the effect of the amount of fatty acid used in the rougher flotation step on the amount of activated carbon required to attain substantial depression of the pulp. When the fatty acid addition was reduced to 0.5 lb. per ton, the recovery in the rougher flotation step remained nearly the same88 percent by weight, or 91 percent iron recovery. As evident from a comparison of the results presented in Table 2 with those in Table 1, the amount of activated carbon required decreased appreciably.

Tests with magnetic taconite concentrate In tests with magnetic taconite concentrate, twelve hundred grams of the magnetic taconite concentrate were floated with 1.0 lb., of fatty acid reagent (Acintol FA-Z) per ton; the rougher froth products thus obtained amounted to 80 percent by weight and analyzed 66.5 percent iron. The froth products were individually used in a hexagonal experiment for the investigation of the effects of the level of activated charcoal addition and the conditioning time on depressant action. The design levels were the same as shown in Table 1, but the ranges of the two factors were changed to 1 to 5 lb. of activated carbon per ton and 3.5 to 10.5 minutes of conditioning time. The iron recovered in the cell product was calculated by taking the rougher froth product as 100 percent.

From these data a second order regression equation was generated using the method of least squares. The experimental error variance was again found to be considerably smaller than the variance due to the lack of fit of the equation, but the multiple correlation coefiicient was sufliciently high (0.95), and the equation was considered to represent the experimental results satisfactorily.

The regression equation and the response contours based on these data show the fatty acid coating on the magnetite concentrate to be effectively removed, and the amount of the activated carbon required appears to be in the same range as that required for the oxidized iron ore. Again, the effect of the conditioning time is not pronounced.

The relation between the amount of the fatty acid collector used in the rougher flotation step and that of the activated carbon required to remove the hydrophobic coating was then investigated. Three series of tests were performed by first preparing the froth products with 0.5 lb. of soda ash and either 1.0, 1.5, or 2.0 lb. of fatty Duplex flotation tests In the flotation upgrading of low grade iron ores, fatty acids (anionic) collectors may be used to float the iron minerals. Quite often, a straight fatty acid flotation, however, does not produce a satisfactory concentrate due to appreciable contamination by the siliceous gangue. Microscopic examination of the flotation concentrate indi cates that the siliceous contaminants are predominantly of fine-sized material. In an amine (cationic) flotation of siliceous gangue the exact converse of the above may be noted, viz., the silica froth is contaminated with fine iron minerals resulting in the lowering of the iron recovery. It is apparent, therefore, that, if the fatty acid collector coating could be removed, the reversed flotation procedure using an amine collector may be applied to float the fine silica contaminant, thereby taking advantage of the marked differences of the floatability between coarse and fine particles in both steps.

To investigate the possibility of applying a two-step anionic-cationic flotation procedure, an oxidized iron ore from the Western Mesabi Range was selected for study. The ore, analyzing 37.3 percent iron, was first crushed through a jaw crusher and rolls to minus 14 mesh. Then a 600-gram sample was ground in a laboratory rod mill for 15 minutes at 50 percent solids, transferred to a Fagergren laboratory flotation cell, and deslimed four times at 20 microns (quartz equivalent) by first dispersing the pulp with 0.5 lb. of sodium silicate per ton. The 15- minute grind rendered the material finer than mesh. The deslimed pulp was transferred to a laboratory conditioner, diluted to 40 percent solids, and conditioned with 0.5 lb. of soda ash and 0.5 lb. of fatty acid reagent (Acintol FA-2) per ton for 3 minutes. The conditioned pulp was then transferred back to the Fagergren cell, floated until barren of froth, and the rougher froth product was returned to the cell and cleaned. The weight percentages of the slime, the rougher tailing, and the cleaner tailing from each test amounted on the average to 12.5, 11, and 6.5 percent, respectively. The cleaner concentrate thus obtained averaged 70 percent by weight and analyzed 44 percent iron, corresponding to 83 percent iron recovery.

The cleaner concentrate coated with fatty acid was then treated with activated carbon to render the surface hydrophilic. The amounts of the surface modifying agent were chosen to be 3 lb. of activated carbon per ton. The conditioning time was fixed at 7 minutes. After conditioning the pulps were observed to be nearly completely depressed.

The amine flotation of siliceous gangue from the conditioned pulp was carried out first by conditioning with Guru 9084, a commonly used starch depressant for iron oxides, for one minute, followed by flotation with a stage addition of an amine salt collector (Armac C) at increments of 0.2 lb. per ton. Usually three to five stages were required either to float the pulp to near completion, or to no further flotation with additional 0.2 lb. of the cationic collector per ton. The cumulative iron recoveries in the flotation concentrate (cell product) and the corresponding grades with the incremental addition of the collector were calculated for each test.

Tests were made in the absence of Gum 9084 and also in the presence of 0.3, 0.6, and 1.0 lb. of the depressant per ton, the fatty acid coating having been removed with activated carbon. The highest selectivity of separation was at 0.6 lb. of Gum 9084 per ton. At this condition a concentrate grade in excess of 62 percent iron making the flotation concentrate hydrophilic were examined. Based on the methods described earlier, the froth products were treated in the following manner and tested for ball quality:

(1) Seven-minute conditioning with 5.2 lb. of activated carbon per ton.

(2) Seven-minute conditioning with 3.4 lb. of activated carbon per ton.

(3) Seven-minute conditioning with 1.7 lb. of activated carbon per ton.

After the treatment listed under (1) the floatability of the material was reduced to less than 10 percent. Treatments (2) and (3) were included to relate the effect of floatability on the ball quality. All the results thus obtained are included in Table 3 for comparison.

TABLE 3.EFFECT OF FATTY ACID COATING AND SUBSEQUENI TREATMENTS FOR ITS REMOVAL ON BALL QUALITY (MAGNETIC TACONITE CONCENTRATE) D "t Moisture Crush, strength, lb. Deformation Slope wet Drop number ti r i rhg. (Percent) (Percent) str./deform.

Wot DPS (lb./.01 in.) 12 in. 18 in. Sui-(gigs? As received:

Test No. 1 9.2 3.2 4.0 5.1 2.2 7.3 3.8 780 Test No. 2.. 8.9 3.5 4.5 5.6 2.1 7.1 4.2 780 Average 9. 05 3. 35 4. 5. 3' 2. 15 7. 45 4. 0 780 Fatty acid floated 9. 5 2. 8 4. 1 6.9 1. 2 8. 6 4. 6 575 Activated carbon:

5.2 lb. per ton 9. 2 3. 4 4.0 5. 6 2.0 8.1 4.2 750 3.4 lb. per ton 9.1 3. 0 4. 3 6.0 1. 6 6.5 4. 1 730 1.7 lb. per ton 9.2 2.7 4.6 6.8 1.3 6.9 4.3 615 is attained with appreciable iron recovery. Certainly, the Activated carbon was found to be quite effective in scavenging of the silica froth is expected to increase the restoring the ball quality in both the crushing strength and iron recovery. the decrepitation temperature. Reducing the amount of Pelletizing studies the activated carbon decreased its effectiveness on the ball The fatty acid coating on iron flotation concentrates i' more or less m parallel Wlth h causes operational difliculties during the firing cycle of Actlvated carbon appears to other apattlcutarty Ptomls' pelletizing, particularly when the green balls are being t hg to the removal of fatty eetd cottmgs from dried. To investigate if certain standard tests for green 0X1 6 Fe both the duplex flotattonprocess ball quality might be capable of characterizing th ff and for pelletizing of flotation concentrates. With its large of the hydrophobic coating, the magnetic taconite con- 40 SPeelhc Shrfaoo m the Order f 00 sq. in. per gram, the centrate was floated with 0.5 lb. of soda ash and 1.0 lb. adsorbed 8.0a!) h are thought to e Wi desorbed of fatty acid reagent (Acintol FA 2) per t and used from the iron oxide surfaces by redistribution over the for balling tesm Although the flotation was nearly enormous surface area of the activated carbon. Indirect plate (the froth product ranged from 97 to 99 percent evidence of this mechanism may be seen In tests which by weight), the from and the cell product were recorm show the amount of activated carbon required for differbined so as not to affect the size distribution. Wet filter eht amehhts of the fatty aetd eoheetor usettto be roughly cake thus prepared, containing 2.27 kilograms of dry conproportional. Cursory electrophoreses exper ments showed centrate was mixed with 1135 grams (0.5 Percent) of that the activated carbon was slightly positively charged bentonite, and balled in an 8.00 x 4-inch airplane tire to hear a t e from h tetattvehf Strong adsorptloh produce /z-inch balls. The balling of the flotation conof the ahtohte eoheetet hhght he ahttetpeted' centrate did not present any notable difiiculties. The as In the duplex hotattoh ptocese the aettvated eahbottm received magnetic taconite concentrate was balled in the Pulp may also adsorb exeeselve amohhteot the ahhhe an identical manner for comparison. collector. The adsorption capacity of the activated carbon The standard tests applied to the green balls were: the for ddeey1ammh1hm eh1hde appeared 'he,strohgly determination of moisture, the determination of wet and dependent 011 P f e neutral pH region it ranged dry strengths with a ball tester, the drop tests both from from to 150 mtthgram? of the collector Per gram 12 and 18 inches, and the decrepitation test. All the test or 10 to 15 Percent by Y h of the ,actlvated carbon results were reported as arithmetic averages on ten bans used. In the present investigationthe amine collector was, except for the decrepitation tests in which twenty wet therefore added stages to ehmlhate as {hhch eahhoh balls were used. The data are presented in Table 3. Durthe y Stages as P 18. The FQI'ISUIDPHOD of amine, ing the determination of the wet strength it was noted however, tho h aPPear to he hoheeajhly excesstve', that the plasticity of the balls, indicated by the slope of general It has been h t th the hehefiefatmh the load-deformation plot, was markedly higher for the o Ores Where e Ore S Sub ected to a primary concentrate floated with fatty acid. These slopes, examomo fatty aold flotatlon, the fatty aold ooatm? may pressed in terms of pounds per 0.01 inch of deformation, removed f the Iron ore concentrate P the were, therefore, calculated and included in the table concentrate in water to about 10 to 50 percent solids and As evident in Table 3, the fatty acid coating reduced odmlxmg about o Q Pounds of aohvatod carbon Per both the wet and dry strength of the balls but increased ton of ore and oondmonmg for about one to 30 mmhtos their plasticity. The increased plasticity was reflected in at temperature between about room temperature and the higher deformation and drop number. The most 60 and P of about 5 to notable change was the lowering of the decrepitation temo fqllowlng 60110111519118 'fl f from tho perature (the maximum gas temperature at which all h investigative Work upon which this invention is based. The test balls survived undamaged in a gas flow of 300 s.c..f.m. Y' QP ngs of fatty acid on oxidized iron ore Square fem) flotation concentrates or on magnetic taconite concen- After the extremes of ball quality had been established 68 may be effectively removed by activated carbon. the effects of various activated carbon treatments on 7 With the oxidized iron ore the fatty acid flotation concentrate can be depressed with activated carbon and further upgraded by the reversed flotation of siliceous gangue with an amine collector. The high adsorption capacity of activated carbon for the amine collector could be alleviated 'by the stage addition of amine. In the pelletizing of the magnetic taconite concentrate the presence of fatty acid collector was shown to affect adversely the wet as well as the dry strengths, to increase the plasticity of the green balls, and, in particular, to lower markedly the 'decrepitation temperature. The activated carbon restored the decrepitation temperature to the original temperature.

I claim:

1. A method of beneficiation of iron ores wherein iron ore is subjected to a primary anionic fatty acid flotation, including removing fatty acid coatings from the finely divided iron ore concentrates resulting from said fatty acid floation, which method comprises:

(A) repulping said concentrates in water,

(B) conditioning by the admixture of activated carbon in the amount of about 0.5 to 10 pounds of activated carbon per ton of ore,

(C) subjecting the conditioned concentrates to further flotation to float off separated fatty acid,

(D) filtering the further flotation concentrate to separate water therefrom,

(E), forming into balls, and

(F) subjecting to heat to pelletize the same.

2. A method according to claim 1 further characterized in that said conditioning with activated carbon is carried on for about one to 30 minutes.

3. A method according to claim 1 further characterized in that said conditioning with activated carbon is carried on at a temperature between about room temperature and 60 C.

4. A method according to claim 1 further characterized in that said conditioning with activated carbon is carried on to a pH of about 5 to 9.

5. A method according to claim 1 further characterized in that said concentrate is pulped to about 10 to percent solids.

6. A method according to claim 1 further characterized in that said conditioned concentrate is subjected to a further cationic flotation to further separate siliceous gangue therefrom.

7. A method according to claim 1 further characterized in that said concentrate is pulped in water to about 10 to 50 percent solids, said conditioning being carried on for about one to 30 minutes at a temperature between about room temperature and C. and to a pH of about 5 to 9.

8. A method according to claim 7 further characterized in that said conditioned concentrate is subjected to a further cationic amine flotation to further separate siliceous gangue therefrom and further upgrade the iron ore.

References Cited UNITED STATES PATENTS 2,496,050 1/1950 Herkenholf 209-166 2,743,172 4/ 1956 De Vaney '-3 2,766,883 10/1956 Chapman 209-166 2,855,290 10/1958 Freeman 75-3 X 3,331,505 7/1967 Mercade 209-166 X FOREIGN PATENTS 1,253,093 4/ 1960 France.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner.

US Cl. X.R. 209-l66 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,430,763 March 4 1969 Iwao Iwasaki It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below: Column 2, line 33, "X first occurrence, should read X Columns 3 and 4,

"facilities" should read facilitates 6, line 3 thereof, "Percent Column 3, line 4, TABLE 2, in the sub-heading to the table, column Fe should read Percent Fe Rec Signed and sealed this 7th day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

